Several simple heterocyclic compounds, such as furans and thiophenes, are known to damage mammalian lung, liver, and kidney. Some of these compounds occur naturally, primarily as smog components, in cotton mill dust, and in certain plants. This project seeks to begin to determine what chemical factors govern the organ specificity of the toxic effects. To this end, several analogues of natural toxins, which differ from them in chemically predictable fashion, are under study. For each, the extent of toxic damage inflicted on lung, liver, and kidney will be determined, as will the distribution of the compound to these three organs. Also, a start will be made toward determining metabolic patterns for the compounds.